This invention relates to an optical disc having a large recording capacity and a high data accessing speed and interchangeable with a current type of optical disc, and a method for recording on the optical disc.
Heretofore, as a write-once or overwrite type data-recording optical disc, an optical disc of the CAV (constant angular velocity) system, in which the disc is rotated at a constant angular velocity, is employed for its superior accessing time and seek time. If the optical disc is used as a recording, medium for an electronic computer, for example, it is necessary to shorten the accessing time required for data recording/reproduction, that is, the data recording/reproduction need to be carried out at an elevated speed. As a measure of the recording capacity of the optical disc, the recording capacity per track is determined by the number of recordable marks at the inner most part of the recording region of the disc.
As a matter of fact, among the specifications for International Organization for Standardization for data-recording optical discs, there are ISO/IEC DP 10090 and ISO/IEC DIS 10089 for a 3.5 inch optical disc and a 5.25 inch optical disc, respectively.
According to the ISO/IEC DIS 10090-CCS system for the 3.5 inch optical disc, the optical disc has a recording capacity of 128 Mbytes per side by recording of 512 bytes per sector. With this optical disc, a large capacity of the recording information may be handled as compared to that handled by a magnetic disc. Among parameters for this system, the track pitch is 1.6 .mu.m, while the reciprocal of the circumferential recording density is 1.0 .mu.m/bit.
According to the ISO/IEC DIS 10089 system for the 5.25 inch optical disc, the optical disc has a recording capacity of 128 Mbytes per side by recording of 1K byte per sector and a recording capacity of 293M bytes per side by recording of 512 bytes per sector. With this optical disc, a large capacity of the recording information may be handled as compared to that handled by a magnetic disc. Among parameters for this system, the track pitch is 1.6 .mu.m, while the reciprocal of the circumferential recording density is 1.0 .mu.m/bit.
These recording data are recorded on the data-recording optical disc in accordance with a recording system which is a combination of the light modulation system and a mark length recording shown in FIG. 1.
Recently, newer electronic computers are capable of handling a large quantity of data at an elevated speed. This information processing capability of the electronic computer is effectively utilized for recording data of results of simulations of larger quantities calculated by the electronic computer on a recording medium while these results are displayed on a real-time basis on a display screen. For fully demonstrating the computer capability to the utmost extent in carrying out the above processing operations, a larger capacity of the optical disc is desired.
Meanwhile, with the CAV system optical disc capable of performing high-speed accessing, the maximum recording density is achieved at the inner most periphery of the disc. However, since the information is recorded by the CAV system on the tracks in their entirety with the same recording capacity for each track, the recording density at the radially outer disc region is lower than that at the radially inner disc region, as a result of which the total recording capacity is lower than that of the optical disc of the constant linear velocity (CLV) system.